The control arrangement of a communication system is the intelligence that acts, generally in response to stimuli such as subscriber requests, to determine the configuration of system resources that is necessary to provide subscribers with desired communication services.
In systems that provide a variety of services to subscribers, it is typically a characteristic of control arrangements that interactions with the system that are required of subscriber terminal equipment to obtain a particular type of communication service are dependent upon the particular service type being sought, and each service type typically requires a different set of interactions. For example, the traditional control software of a telephone electronic switching system typically requires a subscriber to follow a particular protocol to control a standard telephone call, to follow a different protocol to control a conference call, and to follow yet another protocol to control a data call. This characteristic is generally a consequence of the system internally providing each type of service in a different manner, via different system structures each of which typically responds to and returns different stimuli.
A recognized disadvantage in the prior art is that communication systems typically are unable to provide different types of services by means of different mechanisms without making these differences visible to subscribers in their interactions with the system and to the subscribers' terminal equipment. This occurs, in part, because prior art control arrangements view the services differently and often force subscriber terminal equipment, and consequently the subscribers themselves, to also view them differently. This control arrangement characteristic requires that subscribers or their terminal equipment be aware of the types of services being provided, know which services fall into which service types, and remember a number of different interaction procedures to be able to obtain from the system a variety of different services. From the subscriber viewpoint, this makes the systems difficult and sometimes impractical to use. It also unduly complicates the design of subscriber terminal equipment.
While the above-described characteristics are disadvantageous to control apparatuses of conventional communication systems, they become even more so to control apparatuses of integrated services digital networks (ISDNs). Such networks seek to provide subscribers with many types of voice, data and, in some instances, video, communication services in integrated form, i.e., via a common network and a common interface to the subscribers. Yet, internally, the ISDNs provide the various services significantly through different communication handling--for example, call processing--procedures and through different physical subsystems, each one of which is optimized for the requirements of the particular service that it is providing. This makes it difficult to hide the differences from the subscribers and to provide them with an interface to the network that is common for all services and yet is simple.
The evolution of ISDN technology is young, and their system configurations and hardware are often changing. But to present subscribers or their terminal equipment with a new interface to the network with each major redesign of network internals is undesirable.
In summary, what the art requires but lacks is a control arrangement for communication systems in general, and for ISDN-type networks in particular, that presents a common and unvarying network interface to subscribers and their terminal equipment for a variety of services and across many network fabrics.